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Antarctic toothfish, lost – and found

Antarctic toothfish, lost – and found

December 7, 2014

Scientists from the University of Canterbury, the National Institute for Water and Atmospheric Research (NIWA), and the University of Illinois are working together at Scott Base to investigate the disappearance of large Antarctic toothfish from McMurdo Sound, Antarctica.

The project, led by Canterbury’s Dr Regina Eisert, is examining the impact of fisheries and climate change on top predators in the Ross Sea – whales, seals, penguins and toothfish. One key question is whether the Ross Sea fishery for Antarctic toothfish is affecting the seals and whales that eat toothfish.

Antarctic toothfish, large predatory fish that reach two metres long and a weight of over 100 kg, have been studied by scientists in McMurdo Sound for over 40 years, in particular Professor Art DeVries (University of Illinois). Beginning in 2003, Professor DeVries saw a radical drop in the numbers and size of toothfish caught. He proposed that the commercial fishery initiated in the Ross Sea in 1997 had depleted large toothfish from McMurdo Sound.

In contrast, stock assessments for toothfish generated by NIWA scientists and adopted by the Convention for the Conservation of Antarctic Marine Living Resources - based on data collected from the fishery and research surveys throughout the past decade - showed no evidence of a drastic decline. So what about McMurdo Sound?

``Although McMurdo Sound represents only a small area at the southern extreme of the Ross Sea, the area is important habitat for Weddell seals and killer whales, who feed on toothfish during the summer months and may need this high-energy prey to support reproduction,” Dr Eisert says.

She teamed up with two NIWA fish scientists, Dr Steve Parker and Dr Sophie Mormede, and Professor Art DeVries to investigate the issue. Combining Professor DeVries’ several decades' worth of experience of ice fishing in McMurdo Sound with the NIWA scientists' knowledge gained studying the Ross Sea, the team went searching for the missing toothfish. Using a modified vertical line and hooks baited with squid set in a hole drilled through two metres of ice, they sampled both areas fished in previous years and some never fished before, down to depths of more than 600 metres.

The first line in deep water caught six huge toothfish. The second line, hauled the next day, caught six more, including a huge fish weighing 50 kg. Six lines brought in 23 toothfish ranging from 108 to 155 cm in length, precisely the size range absent from McMurdo Sound catches in recent years. Given the abundance of large, mature fish, it is unlikely that the disappearance in McMurdo Sound was caused by the Ross Sea fishery. Ten fish were measured, tagged and released to study movement patterns.

``After the fantastic success of our pilot season, our next goal is to develop a systematic survey of toothfish abundance in McMurdo Sound to reconcile data from this area with the rest of the Ross Sea. We also plan to keep live toothfish at Scott Base to gain important information about their diet, growth, and physiology,” Dr Eisert says.

The project is funded by the Ministry of Primary Industries, with logistics support provided by Antarctica New Zealand.

ends

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